Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
This patch has been successfully tested. All the khugepaged shmem tests passed.
# ./khugepaged khugepaged:shmem
Save THP and khugepaged settings... OK
Allocate huge page on fault... OK
Split huge PMD on MADV_DONTNEED... OK
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table OK
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present OK
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound pages... OK
Collapse PTE table full of compound pages OK
Restore THP and khugepaged settings... OK
Tested-by: Mario Casquero
On Thu, Jun 12, 2025 at 5:55 AM Baolin Wang
wrote:
>
> When running the khugepaged selftest for shmem (./khugepaged all:shmem),
> I encountered the following test failures:
> "
> Run test: collapse_full (khugepaged:shmem)
> Collapse multiple fully populated PTE table Fail
> ...
> Run test: collapse_single_pte_entry (khugepaged:shmem)
> Collapse PTE table with single PTE entry present Fail
> ...
> Run test: collapse_full_of_compound (khugepaged:shmem)
> Allocate huge page... OK
> Split huge page leaving single PTE page table full of compound pages... OK
> Collapse PTE table full of compound pages Fail
> "
>
> The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
> khugepaged from continuing to scan shmem VMA after khugepaged finishes
> scanning in the wait_for_scan() function. Moreover, shmem requires a refault
> to establish PMD mappings.
>
> However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
> set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during
> refault.
>
> To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
> refault.
> With this fix, the shmem test case passes.
>
> Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled
> by the hw/process/vma")
> Signed-off-by: Baolin Wang
> ---
> tools/testing/selftests/mm/khugepaged.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/khugepaged.c
> b/tools/testing/selftests/mm/khugepaged.c
> index 8a4d34cce36b..d462f62d8116 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int
> nr_hpages,
> usleep(TICK);
> }
>
> - madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
> -
> return timeout == -1;
> }
>
> @@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg, char *p,
> int nr_hpages,
> if (ops != &__anon_ops)
> ops->fault(p, 0, nr_hpages * hpage_pmd_size);
>
> + madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
> if (ops->check_huge(p, expect ? nr_hpages : 0))
> success("OK");
> else
> --
> 2.43.5
>
>
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 2025/6/12 23:46, Zi Yan wrote:
On 11 Jun 2025, at 23:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
Can you add the title of the commit? It is easier to understand the context.
2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
Sure.
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during
refault.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int
nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
I assume you are going to just remove this madvise based on your discussion
with David. With that, feel free to add Reviewed-by: Zi Yan
Thanks.
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 12.06.25 17:46, Zi Yan wrote:
On 11 Jun 2025, at 23:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
Can you add the title of the commit? It is easier to understand the context.
2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
Probably checkpatch.pl would point out the same :)
--
Cheers,
David / dhildenb
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 11 Jun 2025, at 23:54, Baolin Wang wrote:
> When running the khugepaged selftest for shmem (./khugepaged all:shmem),
> I encountered the following test failures:
> "
> Run test: collapse_full (khugepaged:shmem)
> Collapse multiple fully populated PTE table Fail
> ...
> Run test: collapse_single_pte_entry (khugepaged:shmem)
> Collapse PTE table with single PTE entry present Fail
> ...
> Run test: collapse_full_of_compound (khugepaged:shmem)
> Allocate huge page... OK
> Split huge page leaving single PTE page table full of compound pages... OK
> Collapse PTE table full of compound pages Fail
> "
>
> The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
> khugepaged from continuing to scan shmem VMA after khugepaged finishes
> scanning in the wait_for_scan() function. Moreover, shmem requires a refault
> to establish PMD mappings.
>
> However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
Can you add the title of the commit? It is easier to understand the context.
2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
> set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during
> refault.
>
> To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
> refault.
> With this fix, the shmem test case passes.
>
> Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled
> by the hw/process/vma")
> Signed-off-by: Baolin Wang
> ---
> tools/testing/selftests/mm/khugepaged.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/khugepaged.c
> b/tools/testing/selftests/mm/khugepaged.c
> index 8a4d34cce36b..d462f62d8116 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int
> nr_hpages,
> usleep(TICK);
> }
>
> - madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
> -
> return timeout == -1;
> }
>
I assume you are going to just remove this madvise based on your discussion
with David. With that, feel free to add Reviewed-by: Zi Yan
Thanks.
Best Regards,
Yan, Zi
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 2025/6/12 19:45, David Hildenbrand wrote:
On 12.06.25 13:37, Baolin Wang wrote:
On 2025/6/12 18:08, David Hildenbrand wrote:
On 12.06.25 05:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged
all:shmem),
Hmm, this combination is not run automatically through run_tests.sh,
right? IIUC, it only runs "./khugepaged" which tests anon only ...
Should we add it there? Then I would probably have noticed that myself
earlier :)
Yes, see patch 2.
Yes, was pleasantly surprised when I found that :)
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound
pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to
prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a
refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the
VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings
during
refault.
Right. It's always problematic when we have some contradicting
information in the VMA vs. pagecache.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are
disabled by the hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char
*p, int nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg,
char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
It's a shame we have this weird interface: there is no way we can clear
VM_HUGEPAGE without setting VM_NOHUGEPAGE :(
Right.
But, do we even care about setting MADV_NOHUGEPAGE at all? IIUC, we'll
almost immediately later call cleanup_area() where we munmap(), right?
I tested removing the MADV_NOHUGEPAGE setting, and the khugepaged test
cases all passed.
However, a potential impact of removing MADV_NOHUGEPAGE is that,
khugepaged might report 'timeout', but check_huge() would still report
'success' (assuming khugepaged tries to scan the VMA and successfully
collapses it after the timeout). Such test result could be confusing.
If we run into the timeout, we return "true" from wait_for_scan(), and
in khugepaged_collapse() returns immediately.
So we wouldn't issue another check_huge() call in khugepaged_collapse().
Did I miss something?
Ah, right. Sorry for the wrong example. Now I'm fine to drop the
MADV_NOHUGEPAGE settiing. Thanks.
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 12.06.25 13:37, Baolin Wang wrote:
On 2025/6/12 18:08, David Hildenbrand wrote:
On 12.06.25 05:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
Hmm, this combination is not run automatically through run_tests.sh,
right? IIUC, it only runs "./khugepaged" which tests anon only ...
Should we add it there? Then I would probably have noticed that myself
earlier :)
Yes, see patch 2.
Yes, was pleasantly surprised when I found that :)
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound
pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to
prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a
refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the
VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings
during
refault.
Right. It's always problematic when we have some contradicting
information in the VMA vs. pagecache.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are
disabled by the hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char
*p, int nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg,
char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
It's a shame we have this weird interface: there is no way we can clear
VM_HUGEPAGE without setting VM_NOHUGEPAGE :(
Right.
But, do we even care about setting MADV_NOHUGEPAGE at all? IIUC, we'll
almost immediately later call cleanup_area() where we munmap(), right?
I tested removing the MADV_NOHUGEPAGE setting, and the khugepaged test
cases all passed.
However, a potential impact of removing MADV_NOHUGEPAGE is that,
khugepaged might report 'timeout', but check_huge() would still report
'success' (assuming khugepaged tries to scan the VMA and successfully
collapses it after the timeout). Such test result could be confusing.
If we run into the timeout, we return "true" from wait_for_scan(), and
in khugepaged_collapse() returns immediately.
So we wouldn't issue another check_huge() call in khugepaged_collapse().
Did I miss something?
--
Cheers,
David / dhildenb
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 2025/6/12 18:08, David Hildenbrand wrote:
On 12.06.25 05:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
Hmm, this combination is not run automatically through run_tests.sh,
right? IIUC, it only runs "./khugepaged" which tests anon only ...
Should we add it there? Then I would probably have noticed that myself
earlier :)
Yes, see patch 2.
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound
pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to
prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a
refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the
VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings
during
refault.
Right. It's always problematic when we have some contradicting
information in the VMA vs. pagecache.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are
disabled by the hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char
*p, int nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg,
char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
It's a shame we have this weird interface: there is no way we can clear
VM_HUGEPAGE without setting VM_NOHUGEPAGE :(
Right.
But, do we even care about setting MADV_NOHUGEPAGE at all? IIUC, we'll
almost immediately later call cleanup_area() where we munmap(), right?
I tested removing the MADV_NOHUGEPAGE setting, and the khugepaged test
cases all passed.
However, a potential impact of removing MADV_NOHUGEPAGE is that,
khugepaged might report 'timeout', but check_huge() would still report
'success' (assuming khugepaged tries to scan the VMA and successfully
collapses it after the timeout). Such test result could be confusing.
I know this kind of case is very rare and may not even be detectable in
tests. At least, I couldn't reproduce it. But I prefer to keep the
original test logic and fix the issue without making further changes.
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 12.06.25 05:54, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
Hmm, this combination is not run automatically through run_tests.sh,
right? IIUC, it only runs "./khugepaged" which tests anon only ...
Should we add it there? Then I would probably have noticed that myself
earlier :)
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during
refault.
Right. It's always problematic when we have some contradicting
information in the VMA vs. pagecache.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int
nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
It's a shame we have this weird interface: there is no way we can clear
VM_HUGEPAGE without setting VM_NOHUGEPAGE :(
But, do we even care about setting MADV_NOHUGEPAGE at all? IIUC, we'll
almost immediately later call cleanup_area() where we munmap(), right?
--
Cheers,
David / dhildenb
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 2025/6/12 13:10, Dev Jain wrote:
On 12/06/25 9:24 am, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound
pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to
prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a
refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the
VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings
during
refault.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem
refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are
disabled by the hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char
*p, int nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg,
char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
The idea looks sane to me, but do we need to add the madvise call to
madvise_retracted_page_tables() too, since that also calls wait_for_scan()?
Yes, I also realized this after sending the patches:) Thanks.
To keep the original logic:
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index d462f62d8116..3452763e2fe3 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1074,6 +1074,7 @@ static void madvise_retracted_page_tables(struct
collapse_context *c,
return;
}
success("OK");
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
c->collapse("Install huge PMD from page cache", p, nr_hpages, ops,
true);
validate_memory(p, 0, size);
Re: [PATCH 1/2] selftests: khugepaged: fix the shmem collapse failure
On 12/06/25 9:24 am, Baolin Wang wrote:
When running the khugepaged selftest for shmem (./khugepaged all:shmem),
I encountered the following test failures:
"
Run test: collapse_full (khugepaged:shmem)
Collapse multiple fully populated PTE table Fail
...
Run test: collapse_single_pte_entry (khugepaged:shmem)
Collapse PTE table with single PTE entry present Fail
...
Run test: collapse_full_of_compound (khugepaged:shmem)
Allocate huge page... OK
Split huge page leaving single PTE page table full of compound pages... OK
Collapse PTE table full of compound pages Fail
"
The reason for the failure is that, it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function. Moreover, shmem requires a refault
to establish PMD mappings.
However, after commit 2b0f922323cc, PMD mappings are prevented if the VMA is
set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD mappings during
refault.
To fix this issue, we can set the MADV_NOHUGEPAGE flag after the shmem refault.
With this fix, the shmem test case passes.
Fixes: 2b0f922323cc ("mm: don't install PMD mappings when THPs are disabled by the
hw/process/vma")
Signed-off-by: Baolin Wang
---
tools/testing/selftests/mm/khugepaged.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/tools/testing/selftests/mm/khugepaged.c
b/tools/testing/selftests/mm/khugepaged.c
index 8a4d34cce36b..d462f62d8116 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -561,8 +561,6 @@ static bool wait_for_scan(const char *msg, char *p, int
nr_hpages,
usleep(TICK);
}
- madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
-
return timeout == -1;
}
@@ -585,6 +583,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
if (ops != &__anon_ops)
ops->fault(p, 0, nr_hpages * hpage_pmd_size);
+ madvise(p, nr_hpages * hpage_pmd_size, MADV_NOHUGEPAGE);
if (ops->check_huge(p, expect ? nr_hpages : 0))
success("OK");
else
The idea looks sane to me, but do we need to add the madvise call to
madvise_retracted_page_tables() too, since that also calls wait_for_scan()?
